How to write a design for several buttons in PyQt5 Python in one setStyleSheet block?

Question

Python

Hello everyone, I'm trying to write an interface in PyQt without QT Designer. I need to set the design for several buttons in one StyleSheet block. (in this case b1 and b2).
groubBox.setStyleSheet doesn't work(

from PyQt5 import QtWidgets,QtGui,QtCore
from PyQt5.QtWidgets import QGroupBox,QHBoxLayout,QVBoxLayout,QPushButton

class Main(object):
    def setupUi(self,window):
        window.setObjectName("window")
        window.setMinimumSize(500,500)
        window.setWindowTitle("My Window")

        self.central = QtWidgets.QWidget(window)
        self.central.setObjectName("central")
        window.setCentralWidget(self.central)
        
        buttonsBox = QGroupBox("select") #группа кнопок

        hbox = QHBoxLayout()
        hbox.addWidget(buttonsBox)
        vbox = QVBoxLayout()
        self.b1 = QPushButton("ok",self.central).setGeometry(100,100,100,30) #первая кнопка
        vbox.addWidget(self.b1)
        self.b2 = QPushButton("cancel",self.central).setGeometry(0,100,100,30) #вторая кнопка

if __name__=="__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = Main()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())